This invention relates to conveying articles and more particularly to conveying lightweight articles susceptible to surface scratching.
U.S. Pat. No. 3,869,843 discloses a system for bulk handling of lightweight articles such as thermoplastic containers, e.g. bottles, upstream of a packout station. The conveying ducts shown therein function quite satisfactorily with most articles, however for sensitive end-use applications where consumer appeal is a prime consideration, visible surface marring or scratching of the articles as a result of rather intense frictional rubbing contact with the conveyor surfaces can present problems. With articles formed of thermoplastic material which has been biaxially molecularly oriented during fabrication to improve impact strength, this problem becomes especially acute. Generally, biaxial orientation involves stretching the material while within a preselected temperature range to align the polymer molecules in the direction of stretch followed by rapid quenching to lock in the stresses developed. When such stretching is carried out in the vertical and horizontal directions in forming a hollow three dimensional article, it has been determined that the resulting improved impact resistance is accomplished at the expense of abrasion resistance in the thickness or z direction. Thus, any substantial rubbing of outer unprotected surfaces of such a molecularly oriented article against another rigid member can cause scratching leaving unsightly, usually powdery white, scuff marks on the outer abraded surfaces. Such scratching has been particularly problematic in fluid pressure conveying of containers such as with the system of the aforementioned patent, especially when transport movement is around a turn where centrifugal force is exerted on the articles.